There are several wireless diversity schemes that are capable of improving quality and reliability of a wireless link. As an example, there is often not a clear line of sight between a transmitter and a receiver in a wireless communication system. Especially in indoor and urban environments, the electro-magnetic signal emitted by a transmitting antenna is reflected along multiple paths (multipath propagation) before it is finally picked up at the receiver. Each reflection can introduce phase shifts, time delays, attenuations and even distortions and the reflections can destructively interfere with the signal itself at the aperture of a receiving antenna. The signal that is picked up by the receiving antenna can thus suffer from a loss in signal strength or quality and interference from reflected signals or signals emitted by other transmitters.
To overcome these problems, antenna diversity schemes are known that use two or more antennas to improve reception or transmission. This can be achieved as the same signal is observed by multiple antennas, each experiencing a different interference environment. While one antenna may experience destructive interference, the other may experience constructed interference, as a consequence of which a robust wireless link can be established. Further, multiple antennas can extract more energy from the electromagnetic field resulting in increased signal strength.
A particular implementation of antenna diversity is MIMO (Multiple Input and Multiple Output), which uses multiple antennas both at the transmitter and the receiver. Using a corresponding communication scheme, the capacity of a wireless communication system can be improved, in particular data throughput, by making use of spatial multiplexing. With this scheme, different data streams are transmitted from different transmit antennas in the same frequency channel. Due to their different spatial signatures, the data streams can be separated at the (at least two) receiving antennas, effectively enabling the transmission of data streams on separate spatial channels at the same frequency. Data throughput can accordingly be increased.
In order to realize the advantages provided by an antenna diversity scheme, a certain distance is required between the antennas of the sending/receiving device. For example in the spatial multiplexing scheme, the receiver needs to separate the signals arriving with different spatial signatures in order to be capable of separating the data streams.
However, space is often a critical issue, in particular for portable devices. In order to separate the antennas by the required distance, the housing of the device needs to have a relatively large dimension, especially when operating at low frequencies. Generally, the housing required to provide the appropriate distance will be larger than required by the electrical circuits enclosed therein.
It is thus desirable to enable the implementation of a antenna diversity scheme, such as spatial diversity or spatial multiplexing, also in small devices. It is further desirable that the two or more antennas of such a device will deliver uncorrelated signals. It is further desirable to adapt the signal reception/transmission by the two or more antennas to the current reception/transmission conditions, such as frequency band, signal strength or quality, data rate, environmental conditions, e.g. the signal paths and the like.
Accordingly, it is an object of the present invention to obviate at least some of the above disadvantages and to provide an improved electronic device configured to enable a multiple antenna communication scheme.